I have a question regarding a 1990 m936A2 wrecker I have while engaging the pto. This is my second m936A2 wrecker I’ve owned and didn’t have this issue with the first one. I first had problems with the transfer case interlock solenoid couldn’t shift the transfer case. I disabled that solenoid by plugging the line going to interlock solenoid to allow me to shift the transfer case. Prior to this I would bleed down air pressure to shift . The problem I am having was with both scenarios. I place transfer case in neutral , engage pto, shift transmission to 1-5 (doesn’t make a difference going to 1-1) and once engine loads up telling me pto is engaged I would slowly increase rpm , in doing so the transfer case would make a chatter, grinding noise and engine would struggle some to increase rpm . What do you think the cause for this is? To me seems as if the gears are clashing or there is something causing strain on the gears .